Following a competitive pitch led by Oystercatchers, Havas Media International will begin working with Source immediately.
Source provides exchange-traded products (ETPs) with almost $20 billion (£13.12 billion) in assets under management. The investment firm offers equity, fixed income, commodity and alternative market exposure through more than 84 ETPs.
David Goodall, managing partner at Havas Media International, said: "The current climate is perfect for Source’s aspiration to create a more efficient market for ETPs in Europe and position itself as the most trusted ETP provider in the sector.
"Havas Media International, through its meaningful communications strategy and excellent understanding of the financial services sector, is the perfect partner to help Source realise its big ambition."
James Polisson, the chief marketing officer at Source, said: "We were extremely impressed with all the agencies who participated in the pitch, but Havas Media International ultimately stood out for us.
"They presented acute insight into the ETP market and innovative strategy to position us in the market successfully."